1. Field of the Invention
The invention relates generally to pumps for use in the hydrocarbon recovery industry, and in particular to a pressure driven pumping system for pumping hydrocarbons from a well.
2. Background Art
Pumps are used for a variety of tasks in the oil and gas industry. In particular, pumps are often used in subsea applications, such as for operating pressure driven subsea equipment (BOPs, gate valves, and the like), for bringing drilling mud to the surface while drilling, and for bringing produced fluids from a completed well to the surface.
Examples of pumping systems are disclosed in various patents. U.S. Pat. No. 6,202,753 discloses an accumulator for use in deepwater operational and control systems. The apparatus uses a differential between a high pressure ambient pressure source such as seawater pressure and a low pressure source such as a chamber holding vacuum or atmospheric pressure to provide storage and delivery of hydraulic power for operation of equipment.
U.S. Pat. No. 6,325,159 discloses a system for drilling a subsea well from a rig through a subsea wellhead below the rig including a wellhead stack mounted on the subsea wellhead. The wellhead stack includes at least a subsea blowout preventer stack and a subsea diverter. A drill string extends from the rig through the wellhead stack into the well to conduct drilling fluid from the rig to a drill bit in the well. A riser which has one end coupled to the wellhead stack and another end coupled to the rig internally receives the drill string such that a riser annulus is defined between the drill string and the riser. A well annulus extends from the bottom of the well to the subsea diverter to conduct fluid away from the drill bit. A pump has a suction side in communication with the well annulus and a discharge side in communication with the rig and is operable to maintain a selected pressure gradient in the well annulus.
U.S. Pat. No. 6,263,971 discloses a system used for production of petroleum effluents situated at great water depths. The system includes an intermediate floating station situated below the surface at a depth selected according to the pressure of the effluent at the outlet of wellheads situated on the station, production risers communicating with the well to be worked, an anchor including production risers, a pump situated on the floating station which transfers the effluent to a processing or destination site, a transfer which transfers the effluent between the floating station, the water bottom and a final platform or a processing plant, and an energy source providing necessary energy to the various equipments installed on the floating station.
One problem with producing fluids through a subsea wellhead is that pressure in the formation generally decreases over time, affecting the demands on the pumping system used to bring fluids to the surface. In particular, it is desirable for the pumping system to be capable of pumping fluid to the surface even when well fluid pressure has decreased below ambient hydrostatic pressure.